This invention relates generally to video cameras, and more particularly to focusing mechanisms for video cameras.
Compact video cameras are available from a variety of manufacturers. For example, such cameras are available from Sony and JVC of Japan. Some models, such as the model TM-540 black-and-white video camera made by Pulnix, are used in manufacturing and inspection equipment to provide a visual input to the equipment.
In FIGS. 1 and 2, a prior art video camera 10 is coupled to a base assembly 12 and includes a main body 14 and a lens assembly enclosed within a barrel 16. As illustrated in FIG. 2, the barrel 16 may slide into and out of the main body 14 along a focusing axis 18 to vary the focus of the lens assembly. An optical detector and video camera electronics (not shown) are located within the main body 14 of the video camera 10. The detector and video camera electronics are powered by a power line 20, and video and control signals are carried on a bus 22.
The main body 14 of the video camera 10 is affixed to the base assembly 12 by engaging the main body 14 with a first U shaped channel member 24 which is affixed to a base plate 26. This engagement can be by a tight compression fit of the main body 14 within the channel shaped member 24, or it may be accomplished by set screws, adhesives, or other fastening techniques. The barrel 16 extends into a second U shaped channel member 28 (which is also affixed to base plate 26) and can move back and forth within the channel member along the aforementioned focusing axis 18. The position of the barrel 16 can be fixed by tightening set screws 30 which extend through threaded bores provided in the sidewalls 32 of the channel member 28.
To focus the lens assembly of the video camera 10, the set screws 30 are loosened and the barrel 16 is moved back and forth along focusing axis 18 until the lens assembly is properly focused on the optical detector of the video camera. The set screws 30 are then re-tightened to engage barrel 16 and fix its position along the focusing axis 18.
There are several problems encountered with this focusing system. For one, it is difficult to accurately move the barrel 16 by hand to provide a proper focus. For applications requiring a very accurate focus, such as integrated circuit lead inspection, the barrel often needs to be positioned as accurately as 20/1000th of an inch to properly focus the lens assembly. Another problem is that each time the set screws 30 engage the barrel 16 they form indentations in the barrel. These indentations can make it difficult to properly fix the position of the barrel 16 after its position has been re-adjusted because the set screws 30 tend to reengage with these indentations. There is also the possibility that the barrel 16 and the camera lens assembly can be damaged by over-tightening the set screws 30.